The present invention relates to a pipe joint for flexible pipes used in the arrangement of gas pipes, water pipes, etc.
There have heretofore been proposed various pipe joints of this kind, such as in Japanese Patent Public Disclosure No. 60-73193, for example. A typical one is shown in FIG. 1. The illustrated prior art pipe joint comprises a joint body 1 provided on one side thereof with a cylindrical portion 5 having an external thread formed on the outer periphery thereof and also provided in the interior thereof with a pipe receiving wall 1a, a cap nut 2 having an internal thread 6 formed in the inner periphery thereof for helically meshing with the male thread on the cylindrical portion 5 of the joint body 1 and also having a proximal end 2a, a retainer 3 provided in the interior thereof with a corrugated portion 7 engageable with the peripheral corrugation of a flexible pipe 9, also provided on one end thereof with a flange 8 of increased wall thickness and adapted to be inserted into the cylindrical portion 5 of the joint body 1, and gasket 4 interposed between the other end of the retainer 3 and the pipe receiving wall 1a of the joint body 1.
The flexible pipe 9 is joined to the pipe joint of the aforementioned construction by the following procedures. The cap nut is inserted about the pipe 9 and, at the same time, the retainer 3 is also inserted about the pipe 9 so that an end face 9a of the pipe 9 projects slightly from the aforementioned other end of the retainer 3 and that the corrugated portion 7 of the retainer 3 is engaged with the peripheral corrugation of the pipe 9. Meanwhile, the gasket 4 is disposed on the pipe receiving wall 1a of the joint body 1. In this state, the internal thread 6 of the cap nut 2 is meshed helically with the external thread on the cylindrical portion 5 of the joint body 1 and then the cap nut 2 is rotated in a predetermined direction until the proximal end 2a of the cap nut 2 collides against the increased wall flange 8 of the retainer 3. Subsequently, the cap nut 2 is further rotated in the same direction by the use of a tool (not shown) to cause the poximal end 2a of the cap nut 2 to push the flange 8 of the retainer 3 toward the pipe receiving wall 1a of the joint body 1. At this time, the flexible pipe 9 engaged with the retainer 3 is also pushed in the same direction. As a result, the projecting end face 9a of the pipe 9 is compressed and tightly clamped between the retainer 3 and the gasket 4, thus joining the pipe 9 to the joint body 1.
In the prior art pipe joint, however, the pushing of the flange 8 of the retainer 3 by the proximal end 2a of the cap nut 2 produces deformation such as distortion etc. on the portion of the retainer 3 other than the increased wall flange 8 and consequently increases frictional resistance between the corrugated portion 7 of the retainer 3 and the peripheral corrugation of the pipe 9 and between the flange 8 of the retainer 3 and the proximal end 2a of the cap nut 2. As a result, the retainer 3 and the pipe 9 kept in engagement with each other are given rotation by rotating the cap nut 2 and are rotated in conjunction with the cap nut 2. Therefore, more rotation of the cap nut 2 than is necessary causes the projecting end face 9a of the pipe 9 rotated in conjunction with the cap nut 2 to twist the gasket 4, thereby lowering the sealing effect of the pipe joint.
Further, since the retainer 3 and the gasket 4 of the prior art pipe joint are made of a conductive material, when the pipe joint is used for pipes buried in the earth, there gives rise to galvanic corrosion and, when the pipe joint is used for such underground pipes in the vicinity of where a railway runs, there gives rise to stray current corrosion. This considerably shortens the service life of the underground pipes and that of the pipe joint.